The present invention relates to a power supply device for an electronic protection unit, suitable for the use in AC/DC power distribution networks at low or medium voltages (i.e. voltages below 100 KV).
It is known that an electronic protection unit is generally used, in a power distribution line, in order to send tripping signals to a tripping device (such as a circuit breaker), which is able to interrupt, if necessary, said power distribution line.
It is also known that an electronic protection unit requires an external power supply device, capable of providing the energy required for its operation.
In particular, it is also known that a very important requirement for an electronic protection unit is to be self-powered. This means that the power supply device of an electronic protection unit must draw the required power from the power distribution line, with which the electronic protection unit is associated. In fact, this allows ensuring high levels of reliability and continuity of service, since a self-powered electronic protection unit allows to perform constant monitoring of the power distribution line and to implement advantageous auxiliary functions.
Examples of power supply devices are known in the state of the art. Electronic protection units for AC power distribution lines adopt, as power supply devices, one or more current-sensing transformers, which are suitable to convert the energy of the magnetic field generated by the power distribution line itself. This technical solution, however, has drawbacks. Although current-sensing transformers are reliable devices, they are very often quite bulky, particularly as the operating voltage rises. Furthermore, they are characterized by high installation costs, which have a severe effect on the final costs of the electronic protection unit.
Furthermore, as it is known, current-sensing transformers cannot be used to supply an electronic protection unit, associated with a DC power distribution line. Therefore, in case of a DC power distribution line different arrangements must be used.
Known devices, which are adopted to supply power electronic protection units for DC power distribution lines, are characterized by drawbacks, too. Practice has shown that these devices are generally capable of supplying an electronic protection unit for relatively low operating voltage values (for example 300 V). This drawback is particularly disadvantageous, since a power supply for much higher voltages is generally required (for example for low-voltage power distribution lines at voltages up to 1 KV, maintaining 12 KV of insulation). This entails the need to provide technical constructive solutions, which are relatively complicated and expensive in order to provide the self-powering of the electronic protection unit and at the same time ensure adequate insulation. Power supply devices for electronic protection units for DC power distribution lines have many difficulties in allowing to supply the electronic protection unit during current transients. This fact entails a decrease in the levels of reliability and continuity of service that can be ensured by an electronic protection unit.